Dynatron receiver



May 2 3, 1933.

P. O, FARNHAM DYNATRON RECEIVER Filed Oct. 17, 1951 Patented May 23, 1933 UNITED STATES PAUL o. FARNHAM, or RooNro-N, NEW JERSEY, AssIGNon To RADIO AMRICA, A. CORPORATION OF DELAWARE PATE-'ANT QFFICB :mrlvifl'lRONv RECEIVER Application filed October 17, 1931. Serial No. 569,422.4

The present invention relates to receiving circuits, andl more particularly to receivers utilizing a dynatron stage adapted for amplication or` oscillation employment.

It is well known that a dynatron will act as a satisfactory oscillator when a tuned impedance of appropriate design, is included in the plate circuit of the dynatron. This `accepteduse of the dynatron as an oscillation generator has restricted the use of the arrangement as an amplifier to circuits employ- -ing an aperiodic plate load. Thls may be explained by the fact that the more usual design requirements for a tuned amplifier are Y freedom from oscillation, as well as freedom from marked variation in gain, as the amplitier is tuned over a range of frequencies. In the case of radio receivers'employing two, or more, tuned amplifier stages in cascade, stability, sensitivity and selectivity of the receiver must be rigidly maintained under all operating conditions. Hence,`when 1t was attempted in the past to employ the dynatron as a tuned amplifier, it was found that known methods of securingA stability were not applicable to the dynatron.

However, in my copending applicatlon Serial No. 523,859, iled March 19, 1931, I have disclosed various methods of, and means for, securing stability of operation of a dynatron amplifier circuit including a tuned plate load impedance. From experimental and theoretical considerations, `the f( llovving characteristics were developed:

When the magnitude of plate load ofv a tuned dynatron amplifier circuit is less than that of the plate resistance (RB 1'), the tube and associated circuits will operate satisfactorily as an amplifier. But, when the external impedance and plate resistance are equal (RBT-'73,), oscillation of the system is impending. Finally, when the load is of greater magnitude than `the plate resistance (RB rp), the system will oscillate. the oscillating condition could be attained either by adjusting the control grid bias t0- ward less negativeA values, or by increasing the plate load.-v Y H Y For utilizing the dynatron as a stable tuned "Q amplifier, the tendency to oscillate, dueto 'comprising at .leastj onel high'frequ'ency dyna- LM. gain control or tuning, was overcome by means which compensated for control electrode bias variation and plate load change.

N ow, I have devised a novel yreceiverarrangement,A embodying and applying the C55 aforesaid principles and observations" disclosed in my said copending: application. There are many situations where it is highly desirable to operate the same radio receiver as an instrumentality Vfor receiving speechleo modulated waves, or chopped continuous waves employed in code transmissions.` VT he change fromspeech to code-reception should Y be eected, of course, with a minimum'use :of apparatus. According tothe present invenl"B5 tion such a 'receiver may be provided byutilizing a dynatron as a tuned radio frequency 'amplilier, when receiving speech modulated energy, and as anoscillation-generator when receiving code signals. l

It may,'therefore, be'lstated that it is Tone oli' the main objects of the present invention toprovide a radio receiver, capable of usefor both code .and speechsignals, the receiver 4475 tron amplifier having a tuned plate load impedance, the amplifierincluding-means `for converting the amplifier into an oscillator Without the addition of further apparatus.

Another .important objectof the present `l` invention is to provide jaV receiver arrangement utilizing a dynatron amplifierv having a resonant output circuit, the receiver including `a device for maintaining an approximately constant` ratio betweenthe'magnitude of 85 the plate resistance and the plateload of a e value to prevent oscillationtvvhen the receiver.

is employed -for speech reception, said device being adapted lfor adjustment to enable said ratio to exceed unity when it is desiredto operate'the dynatron as an oscillator the reception of code signals. Y M .j l

Still other objects of the present invention are to improve generally the simplicity and eiiic'iency of combined broadcalstcode radioreceivers, and to particularly provide such a combined receiverwhi'ch is not only `stable when operating for speech reception,

but converted intoa code-'receiverin an economical and simple manner.

amplification, as -at M1. l*denser 3 is employed for tuning the second rents.l

The novel features which I believe to be characteristic of my invention are set forth in particularity in the appended claims, the invention itself, however, as to both its organization and method of operation will best be understood by reference to the following description taken in connection with the drawing in which I have indicated diagraml'maticallyseveral arrangements for carrying tuned radio frequency amplifier type, wherein a source 1, of speech modulated signal energy, is coupled at M to a tuned radio frequency amplifier stage. The latter may comprise a tetrode of the screen grid type employing an indirectly heated cathode, and is so conventionally represented on the drawing. The input of the stage is tuned by a variable condenser 2.

The output is impressed upon the tuned input of asecond stage of radio frequency A variable constage to resonance'. The tube 4 of this stage maybe a screen grid tube of the same type 'as in the first stage, the control grid 5 thereof being biased by means of the well known biasing network usually disposed inthe grounded lead of the cathode 6. The network consists of a variable resistor 7 shunted 'by a b y-pass capacity 8,`variation of the mag- 'nitude resultingin'change of the gain of the amplifier in a manner well known to those skilled in the-art. The screen grid 9 is connected, by alead 11, to the positive side of a vsource B, the grounded by-pass condenser 12 serving asa path for radio frequency our;

'Ihe Aanode 10 ofthe tube 4 is connected to a point of less positive potential on source B through a path including in series the prilmary coil 13 of a twin winding transformer lM2, a Variable resistor 14, and the adjustable tapv1'5. The negative side of the source B is grounded, whilethe grounded condenser 16 serves to by-pass radio frequency Currents around the source B. The secondary coil 17,

'ofthe transformer M2, is structurally ineluded in the input "circuit ofthe detector tube 18, of the same type as tube 4, the variable condenser 19 serving to tune the detector to resonance. The condensers 2, 3 and 19 are arranged`for mechanical uni-control, as deslgnated by the dotted lines 420, and as em` bodied, for example, in the conventional type of bath tub gang condenser.

The control grid of the detector tube 18 is arranged for detection by providing in the negative lead of the cathode thereof the usual grid biasing network comprising theresistor 7 shunted by the condenser 8.-` The anode of the detector tube is arranged to be positively biased from a sourcel B', the lead between the source and the anode including'th'e coupling resistor 21, the anode circuit of the detector tube being shown arranged for resistance-capacity coupling to the input of an audio vfrequency.'amplifier, not shown. It will be understood that subsequent to audio amplification of the detected energy, the amplified audio energy may be utilized in head-phones, a loud speaker, or any other utilizing means well known to those skilled in the art.

The screen grid of the detector tube 18 is arranged for positive biasingV from asouree S, the positive potential ofthe screen grid being,'of course, considerably'less thanthatapplied to the anode of the detector tube, as is'A l well known to those skilled in the art. The condensers 12 and 16 are employed to bypass radio frequency currents around 'the screen grid and anode leads. l

When the receiver circuit shown in Fig. 1 is v employed for the reception ofvspeech modulated, or radio broadcast, signal energy :the variable resistor 7is lemployed asv thegali'n control mechanism of the receiver. Ithas already been pointed out heretofore that when the tube 4 is. arranged to function in aadynatron circuit (that is when the screen grid has a much higher positive bias than the anode), and the. plate load of -the tube comprises a tuned impedance, there will be a J modulated energy, itis essential -that some device be employed for constantly overcoming the tendency ofthe dynatron stage to "'27 oscillate when the gain control mechanism is adjusted, or when the tuned plate load impedance is varied, as when the output circuit of the dynatron amplifier isvaried with respect toresonance.

In my aforementioned copending applicavtion it has been pointedv out, as stated heretofore, that when the plate load of the dynatron amplifier is less than the plate resistance,

the tube and-associated circuitswill operate Y satisfactorily as an amplifier. Thus, inthe said copending application the tendency to oscillate, if an electrode voltage was adjusted to increase the amplification, .wasiovercme by a simultaneous and-automatic adjustment vof another electrode voltage. Specifically,

this was accomplished by introducing into the Yplate circuit of the dynatron amplifier a regrid bias to avoid conditions favorable for oscillation at any gain control adyustment of the grid bias.y

- `One specific arrangement whereby-this was accomplished in my copending application is shown in Fig. l, it being clearly understood -that this specific arrangement is merely shownby way of illustration, and that any other'methods for overcoming the tendency vto oscillate during gain control of a dyna- 1 tron amplifier are shown in my copendin application. l Vsource B is impressed upon the plate 10 The direct current potential rom through a path, which includes the primary coil 13 ofthe twin winding transformer and the resistor 14, the path having an efectlveV total resistance equal to the aforementioned plate resistance which is to'be introduced .into the plate circuit. The resistor 14 functlons to increase the plate voltage, for a constant plate supply voltage determined by a desired position of the tap 15, as the control grid bias is reduced to increase the stage gain( From Van electrical point of view, and although theresonant circuit 17, 19 is disposed in the input circuit of-the'detectorv tube'18,

- the resonant circuit 17, 19 may be considered 1 as a tuned impedance'which acts as a load on the plate circuit of the vdynatron amplifier. Of course, the value of the resistor 14 is so chosen, and may, for example, have a value of between 15,000 and 20,000 ohms, as to result in securing a stable operation -throughout the variation of the gain control resistor 7.

Reverting to the question of freedom from 4oscillation if the resonant circuit 17,19,

which functions as the load of the dynatron plate circuit, is tuned overa band of frequencies, it is recognized that the impedance, at resonance, of a tuned circuit varies with ,the frequency to which the circuit is tuned.

As the plate load impedance of the dynatron amplifier should vary widely wi th the tuning of the circuit 17, 19, these variations may so alter the magnitude of the load impedance that oscillatory conditions are established. Optimum conditions, so far as concerns stability of operation with tuning, may be obtained by maintaining a constant ratio between the magnitudes of the external plate kload and the internal plate-cathode resistance of the tube. This 'condition may be realized bymaintaining the plate load substantially invariant with tuning for a fixed plate resistance, or by varying the plate resistance as a substantially linear function of a varying plate load.4 The specific arrangement shown in Fig. 1, which comprises vthe path including the resistor 14, functions 'therefore as a compensating or corrective network to carry out the first method which maintains the load impedance, as viewed from the plate and cathode terminals, sub-1 stantially independent of the tuning ofthe output circuit. Thus, itwillv be seen'that once a desired value of plate voltage supply has been determined by adjustingv the 'tap l5 to a desired point, and thev'desired value"A of resistor 14 has been chosen for overcoming the tendency lto oscillate when thefgain of the dynatron stage is varied, or when the plate load is varied by tuning, then the tuned `dynatron amplifier stage will be stable ings() operation.

It should be pointed out'that the first'radio amplifier stage may also comprise af tuned dynatron amplifier stage, and that the twin.

winding coupling transformer M2 may vbefo'85 employed in place of the coupling M1. Further-more, it' is to be clearly understood that -the resonant circuit 17, 19 may be disposed directly in the plate circuit of the dynatron amplifier, a twin winding transformer being @90 employed for the sake of convenience `in securing other desirable advantages which need not be mentioned herein. It is again pointed out that in my aforementioned copending application various other methods lare dis- C95 closed for securing stability of operation, (that 'is overcoming tendency to oscillate, during gain control and `tuningvariation) and it is to be clearlyl understood that' any; of such methods for lsecuring stability of 1D0 operation may be employed herein inV` place of the specific arrangement shown. y

When it is desired to receive codesignals, that is to say code signalsl transmitted inr the form ofchopped continuous waves, itd is merely necessary to allow the'dynatron amplifier stage to oscillate. This maybe accomplished by taking adyantage ofthe observations already described. It is only necessary to vary the magnitude of the resistor no 14 to such a value that it will failto overcome the tendency for the dynatron amplifier to oscillate when the gain control resistor 7 is adjusted rtoward less negative values; 'Of course, it should be realized that sin'iilarlinf'115 stabilitymay be secured by varying the po.- sition of tap 15 on the source B to a'value "proper for oscillation at weak amplitudes when receiving continuous waves. Varia- 'tionof the resistor 14 to give a lower plate 120 voltage will also result in oscillation. ItV

will, therefore, be seen that there are `at least the position of tap 15'to vary' the potential applied to theplate and still another way consists in varying the value of resistor 14 in order to lower the potential applied to 5 the plate 10. The advantage'of decreasing the plate potential, either byvariation of the resistor 14 or by -movement of the tapl, consists in the fact that the dynatron stage then oscillates at such' a part of its charac- 10 teristic that the amplitude of oscillation can be modulated by the incoming signals, thus providing a carrier and side bands for the detector input voltage. Of course, other circuits could be varied to throw a stable dyna- 15 tron amplifier stage into oscillation. In my aforementioned copending application additional variables have beendisclosed which may be controlled to insure stability of a tuned dynatron amplifier, and, accordingly,

' 20 by varying these factors, oscillations may be produced. c A

An aperiodic reactive network is employed in the control grid circuit of the detector tube 18 to prevent overloading of the detector when the precedingA dynatron stage is thrown into oscillation. The network preferably comprises a resistor 23 in series in the control grid circuit, the resistor being shunted by an audio frequency by-pass condenser 22. i One of the important advantages secured by means of the present invention comprises the fact thatv detuning vof the cascaded stages when a gang condenser 1s eml ployed is not produced. Furthermore, the

use of a separate oscillatorl tube. and aV separate tuned circuit, which has been necessary to avoid detuning, is eliminated by means of the present invention.

In Fig. 2 there is shown in diagrammatic manner a superheterodyne receiving circuit .embodying the present invention. It isv not believed necessary to point out the Vdetails vof the circuit in Fig. 2 inspecific manner, in View of the fact that the operation thereof is'substantially the same as the operation of Vthe receiver shown in Fig. 1. It is merely Adensers of each of these receiver elements.

The intermediate vfrequency amplifier is shown as comprising only a single tuned Adynatron amplifier stage, and it is to be understood that the stage corresponds in every way to the second radio frequency amplifier stage of Fig. 1, withthe exception that lthe condenser 3 in the input of the tube 4 is fixedly tuned to the intermediate frequency,

insteadof being arranged for adjustment yas inthe case ofFig. 1.

v'The second detector has itsinput. arranged in substantially the same manner as the detector shown in Fig. 1, with. theexception that th-e condenser 19 is maintained fixedly tuned) to f theA intermediate frequency employed, instead of being adjustableas is the case with condenser 19 and the case of Fig. 1. When receiving speech modulated signalenergy the'superheterodyne receiver in Fig2 functions in the usual manner, the intermediate frequency amplifier being arranged for stable op-eration byladjusting the plate supply voltagel to the desired constant-value by means of the tap 15, and assigning to the resistor 14 the value necessary to.:overcome the tendencyto oscillate when the gain control resistor 7 is adjusted to' vary the amplification, it beingunderstood that the variable resistor 7 vfunctions as the gain'l control mechanism of the superheterodynereceiver.

When it is desired to receive code signals transmitted as continuous waves, it is merely necessary to utilizeany of the three aforementioned methods for throwing the intervmediate frequency'amplifier into oscillation.

Assuming, then, that the resistor 14 is varied to decrease the value of the plate voltage of the tube 4 of the intermediate amplifier, the

tube will oscillate and function tofeed `into the second detector carrier oscillations of intermediate frequency, Whose amplitude Vis modulated by the incoming signals, thus providing va-carrier and-side bands for detection. It will thus be` seen that when the present invention is employed in asuperheterodyne receiver, and when the receiver is employed for receiving continuous Waves, ythe necessity for a separate oscillator between the first and 'second detectors is-rendered unnecessary by throwing the intermediate frequency-'dynaktron amplifier into oscillations.'v

While'I have indicated and described several systems for carrying my invention into effect, it will be vapparent to one skilled in the art that my invention is by no means limitedto the particular organizations shown "and described, but that many modifications may be made without departing from' the scope of Vmy vinvention as set forthin the appendedclaims.l a

What I claiinisz.l 'i'. p y 1. In a v'dynatron a'mplifier,'thev combination with an electron tube and means for applying to the elements thereof potential effective to give the same a negative plate resistance, of a tuned circuit vconnected to the plate'electrode of the tube, means rendering the ratio of plate load impedancefto plate. resistance less than unity when amplifying speech modulated signal energy, said last means being adjustable vto renderl saidratio, greater than unity when amplifying unmodulated carrier Waves.

2. In a radio receiver a dynatron amplifier including a tuned impedance in its output circuit, means for controlling the gain of the amplifier, means for stabilizing the amplifier against oscillation throughout adjustment of said gain control means, said stabilizing means being variable for rendering the amplifier unstable to convert it into an oscillation generator.

3. In combination, in a radio receiver, a high frequency amplifier', a detector coupled to the amplifier, said amplifier including a dynatron circuit provided with. a resonant plate load in the output circuit of the dynatron, means for controlling the gain of the dynatron, a stabilizing means in the output circuit of the dynatron, and additional means for rendering the dynatron unstable to produce oscillations.

4. In a superheterodyne receiver, means for producing intermediate frequency energy, an intermediate frequency amplifier comprising a dynatron circuit provided with a resonant impedance in its output circuit, a detector having its input coupled to said resonant impedance, means for controlling the gain of said dynatron amplifier, means for preventing oscillation of said dynatron amplifier during variation of the gain control means, said oscillation prevention means being adjustable to render the dynatron amplifier unstable to produce oscillations When receiving continuous Waves.

5. In combination, a high frequency amplifier and detector, said amplifier including a dynatron amplifier circuit in its last stage, means controlling the gain of said dynatron amplifier circuit, stabilizing means in the output circuit of the dynatron amplifier circuit, additional means rendering the dynatron unstable to produce oscillations, means in the detector circuit rendering said detector sensitive to the reception of amplified signals When the dynatron circuit is in a non-oscillating condition, and means in the detector circuit preventing overload of said detector when the dynatron circuit is put into an oscillating condition for the reception of chopped continuous Waves.

6. In combination, a high frequency amplifier and detector, said amplifier including a dynatron amplier circuit in its last stage, means controlling the gain of said dynatron amplifier circuit, stabilizing means in the output circuit of the dynatron amplifier circuit, additional means rendering the dynatron unstable to produce oscillations, means in the detector circuit rendering said detector sensitive to the reception of amplified signals when the dynatron circuit is in a non-oscillating condition, and means in the detector circuit preventing overload of said detectorrwhen the dynatron circuit is put into an oscillating condition for the reception of chopped continuous Waves, said last means comprising a resistor in the detector grid circuit, and an audio frequency by-pass condenser in shunt with the resistor.

7. In combination, a high frequency amplifier and detector, said amplifier including a dynatron amplifier circuit in its last stage, means controlling the gain of said dynatron amplifier circuit, stabilizing means in the output circuit of the dynatron amplifier circuit, additional means rendering the dynatron unstable to produce oscillations, means including la bias resistor in the detector cathode and an audio frequency by-pass condenser in shunt With the resistor, in the detector circuit rendering said detector sensitive to reception of vamplified signals when the dynatron circuit is in a non-oscillating condition, and means in the detector circuit preventing overload of said detector when the dynatron circuit is put into an oscillating condition for the reception of chopped continuous Waves.

8. ,In combination, a high frequency amplifier and detector, said amplifier including a dynatron amplifier circuit in its last stage, means controlling the gain of saiddynatron amplifier circuit, stabilizing means in the output circuit of the dynatron amplifier cir-V cuit, additional means rendering the dynatron unstable to produce oscillations, means including a bias resistor in the Vdetector cathode and an audio frequency by-pass con- 

